Quality Assurance and Bioeffects

The routine, periodic evaluation of an ultrasound system to guarantee optimal image quality

Quality Assurance

The AIUM recommends that all equipment should be evaluated and calibrated ______

annualy

why is Quality Assurance important?

1. ensure optimal imaging

2. ensure saftey to pt and sonographer

3. legal reasons

Requirements of QA

1. assess system components

2. repairs as needed

3. preventive maintenance

4. record keeping

Goals of QA

1. guarentee proper operations of the system

2. detect gradual changes

3. minimize downtime

4. reduce number of non-diagnostic exams

5. reduce number of repeat scans

Methods of QA

1. test under known, defined conditions

2. use constant imaging settings

3. use a phantom

4. image in an identical enviorment

Devices used for QA

1. tissue equivalent phantom

2. doppler phantom

3. slice thickness phantom

4. AIUM 100mm test object

Tissue equivalent phantoms are used to evaluate ___ and ____

gray scale and tissue texture

what kind of phantom is the most common

doppler phantoms (flow phantoms)

3 types of doppler phantoms

1. vibrating string

2. moving belt

3. flow phantom

slice thickness refers to the beam thickness ___ to the scanning plane

perpendicular

slice thickness determines ____ resolution

elevational

thicker slices diminish ____ resolution and reduces ability to distinguish low contrast reflectors

spatial

minimum sensitivity

how well the system detects and displays very weak amplitude echoes (TGC is zero and slowly increased until pin is seen)

normal sensitivity

acts as a baseline setting for all performance measures

maximum sensitivity

sets output power and amplification to the maximum practical levels

why is there a dead zone

ringing and switch from send to receive

____ frequency transducers have a thinner dead zone

higher

registration accuracy

1. range accuracy

2. horizontal/verticle depth calibration

3. distance measurement accuracy

axial resolution

smallest distance between 2 objects placed parallel to the sound beam can be distinguished as 2 echoes

lateral resolution

ability to distinguish 2 closely spaced structures that lie side by side or perpendicular to the sound beam

the system’s ability to display similar reflectors in the phantom with echoes of equal brightnes

uniformity

hollow structures should be displayed as ____

anechoic

solid structures should be displayed as _____

hyperechoic

positive

test predicted disease

negative

test predicted absence of disease

true positive (TP)

comparison test is correct, both are positive for disease

True Negative (TN)

comparison test is correct, both are negative for disease

False Positive (FP)

test says there is disease when there is not

False Negative (FN)

test says there is no disease when there is

Sensitivity

ability of a test to detect disease

specificity

ability of a test to detect absence of disease

Sensitivity Equation

sensitivity = TP / (TP + FN)

Specificity Equation

specificity = TN / (TN + FP)

Positive Predicitive Value

how often test is correct when positive for disease

Positive Predicitive Value Equation

PPV = TP / (TP + FP)

Negative Predictive Value

how often test is correct with negative for disease

Negative Predictive Value Equation

NPV = TN / (TN + FN)

Accuracy

% of exams that agree with gold standard

Accuracy Equation

(TP + TN) / (TP + TN + FP + FN)

placed in the sound beam and the oscilloscope displays the sound beams pressure

hydrophone (microprobe)

hydrophone measures pressure at _________

specific locations within the beam

calibrated hydrophone

aligns PZT voltage and acoustic pressure signal

radiation force

measured sound beams power by measuring pressure

acousto-optics

uses light to view soundwaves shape

a shadow system that can be used to show the interaction of sound beams and light

schlieren

3 devices that measure absorption

1. calorimeter

2. thermocouple

3. liquid crystal

calorimeter

measures total power in the entire beam

thermocouple

measures power of a specific area of the beam

liquid crystal

color changes as a result of temperature change gaining info about the sound beam strength

dosimetry

science of identifying and measuring the characteristics of an US beam that are relevant to its potential for producing biologic effects

who regulated output limits in diagnostic ultrasound

Food and Drug Administration (FDA)

who collects data about the regulations on output limits in diagnostic ultrasound

American Institute of Ultrasound in Medicine (AIUM)

in vivo

in the living

in vitro

in glass

AIUM says in vitro bioeffects are real but ____

dont apply to clinical setting

mechanistic approach to study bioeffects

propose theory, then study the effects

empirical approach to study bioeffects

analysis of existing data

TIC

tissue heating at cranial bone

current limit on SPTA

720 mW/cm² SPTA

cavitation is most likely to occur in the ______

lungs

Mechanical Index Equation

MI = peak rarefaction pressure / square root of frequency

epidemiology

population studies in medicine, empirical approach

prospective

forwards looking